In the field of vehicle seats, it is known to detachably attach a rear end of a seat cushion to the floor of the vehicle and pivotally attach a front end of the seat cushion to the floor so that the seat may be retracted by folding the seat back onto the seat cushion, and tilting the folded seat forward around the front end of the seat cushion. In a known vehicle seat, a rail device is provided immediately under the seat cushion frame, and the bottom end of the rail device is fitted with a lock device which is configured to detachably engage a striker fixed to the floor of the vehicle. See JP2011-207257A, for instance.
In such a vehicle, the rail device and the lock device are required to have a high level of mechanical stiffness so that the rail device and the lock device may not deform under the inertia force of the seat and the vehicle occupant at the time of a vehicle crash. Therefore, the weight of the seat is undesirably great, and the manufacturing cost of the seat is undesirably high.